Base fuze

ABSTRACT

1. A hollow projectile having an explosive charge therein, said projectile having a rearwardly facing portion with an aperture formed therein, a closure plate for said aperture, a proximity fuze carried by said closure plate and including an oscillator and an antenna in the form of a conical structure projecting rearwardly from said closure plate, mounting means on said closure plate for supporting the remainder of said proximity fuze within said hollow projectile, and connecting means including a plurality of tapered pins engageable with and passing through said closure plate for electrically coupling said oscillator and antenna with the remainder of said proximity fuze.

States atent 1 olbinson, Jr.

[4 1 Mar. 27, 1973 BASE FUZE [75] Inventor: Ralph 0. Robinson, Jr., Silver Spring, Md.

[73] Assignee: The United States of America as represented by the Secretary of the Navy [22] Filed: Dec. 28, 1956 [21] Appl. No.: 631,382

OTHER PUBLICATIONS Primary ExaminerBenjamin A. Borchelt Assistant ExaminerTh0mas H. Webb Attorney-Q. E. Hodges and Q. B. Warner EXEMPLARY CLAIM 1. A hollow projectile having an explosive charge [1.8. C] P therein projectile having a rearwardly facing por- [51] Int. Cl ..F42c 13/04, F42c 13/00 tion with an aperture formed therein, a closure plate [58] Field of Search ..102/70.2 for said aperture, a proximity fuze carried by said closure plate and including an oscillator and an antenna [56] R f n Cit d in the form of a conical structure projecting rearwardly from said closure plate, mounting means on UNITED STATES PATENTS said closure plate for supporting the remainder of said 1 769 203 7/1930 Buckle 102/70 2 P proximity fuze within said hollow projectile, and con- 2293949 8 I19 42 Potter y "102/70'2 P necting means including a plurality of tapered pins engageable with and passing through said closure plate FOREIGN PATENTS OR APPLICATIONS for electrically coupling said oscillator and antenna with the remainder of said proximity fuze. 91,592 2/1938 Sweden "102/702 P 585,791 2/1947 Great Britain 102/702 P 1 Claim, 4 Drawing Figures OSCILLATOR zs I02 56 66 ENERGIZER 2+ 62 so \i 3; L? ExPLcswE L 44 08% 52 189 54 i i 4 74 9a 19 82 89 E190 .95 I I [85 some msrsn 508/- 77 I36 I88 I 71/ 2a [Ki 92 I94 72 w 2 07 439 I126 72 73 T 137 190 #95 1 as BASE FUZE This invention relates generally to fuzes for use with ordnance projectiles, and more particularly it pertains to radio proximity fuzes mounted in the base of a projectile for exploding military projectiles in the proximity of a target.

Proximity fuzes mounted in the base of a projectile have been of interest since 1942 when it was noted that the radiation maxima of an end-excited projectile tended to bend away from the source of excitation to an increasing degree as the frequency of radio frequency excitation was increased. Hence, there exists for each size of projectile an upper frequency limit beyond which conventional nose-type radio proximity fuzes cannot be employed effectively.

It is apparent from this that if the source of radio frequency excitation is placed in the base of the projectile, the upper frequency limit can be extended by a considerable amount, and further, a more favorable distribution of radio frequency radiation, that is, of a more forward-looking nature, can be obtained.

The earliest interest in radio proximity fuzes mounted in the base of a projectile was created by their potential counter-countermeasure characteristic because of the simple frequency spread method. Later in World War II, as enemy countermeasures failed to materialize, the active interest in an operational base fuze declined.

More recently, however, when it became apparent that rain and clouds were imposing severe limitations on the effectiveness of radio proximity fuzes, interest in adapting radio proximity fuzes for installation in the base of a projectile was re-emphasized because of the possibility that this type of fuze might give better performance under adverse weather conditions by virtue of its protected position at the rear of the projectile. For this reason, a development program was initiated with a major objective of ascertaining whether or not a weather superiority existed for this type of fuze.

In December, 1948, a report was issued in which a preliminary design of a spike antenna fuze for the base of a projectile was described. Initial tests of this fuze in the 90 mm antiaircraft gun indicated satisfactory performance. No great difficulties were anticipated in transferring the testing of this fuze to 5 inch/38 Naval guns. Therefore, it appeared that a radio proximity fuze for the base of a projectile suitable for rainoperability' comparison tests with nose types of radio proximity fuzes was imminent.

Because of the relatively small field of experience in the design of a radio proximity fuze for the base of a projectile, and the large numbers of possible technical approaches to the problem, a program of investigation was undertaken along these lines. The course of investigation undertaken was directed toward attaining components compatible with good fuze operation, as well as service ordnance requirement. This investigation culminated in the present radio proximity fuze for the base of a projectile.

Several advantages result from this new position of the fuze in the base of a projectile, notably protection from rain and atmosphere friction. It is well known that rain can create disturbances of the operation of proximity fuzes due. to the conductive layerthus produced on the outer surface. of the fuze which may seriously load the radiating system of the fuze, and the impacts of the individual raindrops also produce microphonic disturbances. Atmospheric friction is also a disturbing influence as it may cause undue heating, with various undesirable consequence to the efiectiveness of the fuze.

By locating the fuze in the center of the projectile base, these disadvantages are eliminated. The reason for this is that the fuze is immediately behind the much wider base of the projectile and is thus protected from rain and atmospheric impact.

A difficulty encountered in locating the fuze in the base of the projectile is that in such position the fuze is exposed to the full pressure developed in the gun tube by the propellant when the projectile is fired. This necessitates special structural changes and precautions, not needed in conventionally located radio proximity fuzes.

An object of the invention, therefore, is to provide a radio proximity fuze for the base of a projectile.

Another object of this invention is to provide a structure wherein the radio proximity fuze is fitted to f withstand the unusual stresses to which such fuzes are subjected on firing them from a gun.

A further object of this invention is to provide means for preventing leakage of combustion gases into the radio proximity fuze.

A still further object of this invention is to provide means for preventing the base radio proximity fuze from unscrewing while being fired from a gun.

An additional object of this invention is to provide insulated feed-through electrical conductors for connecting the electrical parts of the base radio proximity fuze within the projectile.

It is another object of this invention to provide a proximity fuze for the base of a projectile for use in military projectiles of various sizes and shapes.

Still another object of this invention is to provide a radio proximity fuze for the base of a projectile which is constructed of materials and shapes of plastics capable of withstanding the acceleration, bore pressure, and heat experienced at the base of a projectile.

And still another object of this invention is to provide a radio proximity fuze for the base of a projectile which will give better performance than a nose-mounted radio proximity fuze under adverse weather conditions by virtue of its protected position at the rear of the projectile.

And even another object of the invention is to provide a radio proximity fuze for the base of a projectile in which the source of excitation is placed at the base of the projectile, with the result that the upper frequency limit can be extended by a considerable amount.

To provide a radio proximity fuze in the base of a projectile in which there is a more favorable distribution of the radio frequency radiation, that is, of a more forward-looking nature, is still another object of this invention.

Other objects and many of the attendant advantages of this invention will be appreciated readily as the same becomes understood by reference to the following,

detailed description, when considered in connection with the accompanying drawing in which:

FIG. 1 is a fragmentary elevation of the base end of a projectile having the radio proximity fuze applied thereto, with the upper half of the figure being in axial section;

FIG. 2 is a corresponding end view of the radio proximity fuze illustrated in FIG. 1;

FIG. 3 is a schematic of the electrical circuitry for the radio proximity fuze of FIG. 1; and

FIG. 4 is a longitudinal section, partially in elevation, of the radio proximity fuze having a cap mounted thereon for protecting the fuze in the bore of the gun.

Referring now to FIG. 1 of the drawings, there is illustrated the rear end portion of an ordnance projectile having a fuze 12 of the radio proximity type mounted in its base 14. The projectile 10 has a conventional rotating band 16 located at the base 14 thereof. The projectile 10 has a thickened wall portion 18, and an end portion 20 having a recess 21 in its base 14. Between the thickened wall portion 18 and the end portion 20 of the projectile 10, there is a threaded shoulder portion 22 for receiving a base insert 24. The fuze 12 is supported in the projectile by the base insert 24.

As seen best in FIG. 1, the fuze 12 consists of an oscillator 26 which is mounted external to the contour of the projectile 10. Insulated electrical leads (not shown) are passed through taper pin feed through elements 28 (only one of which is shown) in the base insert 24 into the interior of the projectile 10.

On the interior of the projectile 10, there is a cavity 30 for receiving an explosive charge 56 (shown in FIG. 3) and the other components of the fuze 12, namely an energizer 34, an amplifier 36, a rear fitting 38, an auxiliary detonator 40, and a tetyrl pellet 41, in that order from left to right, as shown in FIG. 1. These elements are contained in a sleeve 275 which is threaded to the insert 24, and secured in position by sleeve pins 240, as shown in FIGS. 1 and 2. Prior to further discussing the mechanical arrangement of the fuze 12, the electrical system will now be described.

Referring now to FIG. 3 of the drawings, there is illustrated a schematic of the circuitry for the fuze 12. The fuze 12 consists of an antenna 42, the oscillator 26 having a triode tube 44, the energizer 34, the amplifier 36 consisting of two pentode tubes 46 and 48, a triode tube 50 and a thyratron 52. The output of the thyratron 52 is connected to an electrical squib 54. The squib 54 is utilized to set off the auxiliary detonator 40 which, in turn, ignites the tetryl booster 41 to explode the main explosive charge 56 contained in the projectile 10.

The oscillator 26 employs a modified Colpitts circuit. The plate 60 of the tube 44 is connected by lead 62 to one terminal of a tank coil 64, and to the antenna 42 by a lead 66.

The other end of the tank coil 64 is connected by a lead 68 to one plate of a DC oscillating capacitor 70 and the other plate thereof is connected by a lead 71 to ground 72.

The grid 74 of the oscillator tube 44 is connected by leads 76 and 77 to ground 72. The filament 78 of the oscillator tube 44 is connected through RF choke 80 to ground 72 by leads 84 and 77. In addition, the other lead of the filament 78 is connected through RF choke 82 by leads 86 and 87 to a battery 89 and thence to terminal 88 located between the two sections 90 and 91 of the battery energizer 34. The electrical lead 92 from the tank coil 64 and the lead 86 from the oscillator tube 44 are passed through the taper pin feed-through elements 28, as indicated by dotted lines in FIG. 3, and illustrated in the base insert 24 in FIG. 1. One end of lead 92 is connected between the tank coil 64 and the oscillating capacitor and the other end is connected to the control grid 94 of the first pentode tube 46 of the amplifier 36 through a resistor 96 and two capacitors 98 and 100.

The plus terminal 102 of the section 91 of the energizer 34 is connected by leads 106, 108, and 112 to the plates of the pentode tubes 46 and 48, and the thyratron tube 52 through resistors 114, 116, and 118, respectively. The plate of the triode 50 is connected by leads 120, 122, 110 and 106 to the plus terminal 102 of section 91 of the energizer 34, through a capacitor 123 and resistor 1 16.

The terminal 88 of the energizer 34 is connected by leads 126, 128, 130, 132, 133, 135, 137 and 86 to the filaments of the pentode tubes 46 and 48, the triode tube 50, and the thyratron tube 52. The negative terminal 136 of section 90 of the energizer 34 is connected by a lead 138 through a resistor 140 to the control grid 142 of the thyratron tube 52.

The screen grid 144 of pentode tube 46 is connected by leads 146, 147 and 148 through resistors 150 and 152 to the leads 106 and 126. The plate 154 of the pentode tube 46 is connected by lead 156 through a capacitor 158 to the control grid 160 of the pentode tube 48, while the plate 62 of the pentode tube 48 is connected by lead 122 through capacitors 123 and 168 to the control grid 142 of the thyratron 52.

The screen grid 170 of pentode tube 48 is connected by leads 172, 174, and 176 through a resistor 178 and a capacitor 180 to leads 106 and 126. The control grid 182 of triode 50 is connected to the plate 181 thereof by a lead 184.

The plate 185 and filament 186 of the thyratron 52 are connected by leads 189, 190 and 137 to a capacitor 192 and an inductor 194 and these elements, in turn, are connected by leads 188 and 195 to the squib 54, as previously mentioned.

It is to be noted that a plate load resistor 199 is located within the amplifier 36 rather than in the oscillator in order to simplify the latter section of the fuze 12. In this way, only two insulated leads 92 and 86 and a ground lead 71 are necessary for operation of the oscillator 26.

Referring again to FIGS. 1 and 2 of the drawings, the fuze components, including the base oscillator 26, the energizer 34, the amplifier 36, the rear fitting 38, and the auxiliary detonator 40 are all components representing geometrical figures of revolution which either plug together or are constrained by threaded sections.

Since the fuze 12 is subjected to severe rotational acceleration upon being fired from a gun, a problem of preventing rotational movement is inherent. In FIGS. 1 and 2, there is illustrated the solution to this problem in which insert locking pins 201 are used to lock the insert 24 in position; with four insulator anti-rotation pins 204 being used to hold the housing 221 in position. A retaining ring lock screw 238 is used for holding the retaining ring 210 in position.

It is to be noted that the base 14 of the projectile is presented to the explosive gases and that the initial acceleration is applied in a clockwise direction. Hence, those -sections of the fuze 12 which screw in from the rear will tend to be tightened by providing left-hand threads.

The threads are made of such hand that upon spin of the projectile they tend to become screwed up more tightly, that is, they must be of the opposite hand from the corresponding threads of a conventional front-end fuze. As pointed out, staking" pins are inserted where desirable to prevent loosening of the threads.

Gas leakage is a problem of paramount importance of the base radio proximity fuze 12. Since this base fuze 12 is to be subjected to the full bore pressure of a 5 inch/38 Naval gun, a number of gas seals can be incorporated in the fuze. These are shown in FIG. 1 as an antenna cap concentric ring gas seal 212, a teflon housing concentric ring gas seal 214, a lead gas seal 216, and the taper pin insulated feed-through insulator 218. The seals can be made of soft metal, preferably metallic lead, or of suitable plastic materials. These seals serve to prevent leakage of combustion ga'ses into the body of the fuze 12 or into the projectile 10 itself.

The type of base radio proximity fuze 12 shown requires that the plastic housing 221 survive mechanically, protect the oscillator components from mechanical damage, and support the cap of the antenna 42 in an electrically efficient and mechanically stable manner. Further, it is desirable that the housing 221 introduce a minimum of electrical losses to the fields of the reaction oscillator 44. 4

Since electrical and mechanical considerations had to be satisfied to the extent of the fuze 12 being both proximity sensitive and safe in the bore of the gun, appropriate electrical and mechanical tests were performed as the design of the fuze progressed. In the development of the oscillator housing 221, a mechanical design was developed which would give a high order of mechanical success and in which the reaction oscillator 26 could give at least a moderate electrical performance. With a later attainment of satisfactory fuze operability at service charge ,in the 5 inch/38 Naval gun, both the electrical and the mechanical designs could be optimized in consideration of actual production requirements.

The choice of an adequate plastic material for the housing 221 involved finding one with mechanical properties suitable for withstanding the eflects of bore pressures of 40,000 p.s.i. andfla me temperatures of the order of 3,000 K. for durations of about 10 milliseconds. These mechanical properties were required in addition to the usual ones of tensile strength and resistance to thermal and mechanical shock, resistance to water absorption, good aging properties, and being chemically inert.

Since one primary function of the housing 221 is to protect the reaction oscillator 26 and support its antenna 42, the plastic had to have a low loss factor. These latter properties had a strong bearing upon the efficiency of the antenna 42 for a given configuration of fuze 12 since they determine to a large extent the ratio of internal to external losses of a given antenna configuration.

A series of mechanical survival experiments were performed in which linen. base bakelite, lucite, polyethylene, and teflon plastic oscillator housings 221 were attached to the base of 5 inch projectiles and fired at service bore pressurein the 5 inch/38 Naval gun. These housings had large, extremely ruggedv antenna caps 42 which may have given some measure of mechanical support. They contained inert reaction oscillators 26.

From the experiments, it was proved that a plastic oscillator housing 221 having the relatively thin wall of a conventional Mark 53 radio proximity fuze front case and containing only an inert oscillator potted in wax would survive mechanically when fired at service charge in the 5 inch/38 Naval gun as shown by microflash photographs taken along the trajectory. For example, ethylcellulose housings 221 withstood between 26,000 and 36,000 p.s.i. pressure in a gun bore.

The over-all external protrusion of the fuze 12 was arbitrarily set at a figure of 2% inches on the basis of practicality from the viewpoint of service handling and reaction oscillator-antenna operation.

Initially it was planned that the base fuze 12 should protrude only 1% inches beyond the rear of the projectile 10 in the interest of ease of handling and stowage aboard ship. However, tests of a considerable number of reaction oscillators 26 indicated that with the slightly greater protrusion of 2% inches, it was possible to achieve 20 to 35 percent greater reaction sensitivity with approximately the same radio frequency circuitry.

The reaction oscillator 26 was designed with modest electrical requirements in that the maximum requirement imposed for the initial design was a reaction sensitivity of approximately 350 MV within an operating frequency of from to MC.

One complicating design factor, however, was the mechanical environment in which the reaction oscillator 26 was to be located with the physical constraint of occupying a minimum volume. Undoubtedly the mechanical problem could have been greatly minimized with the design of a tougher oscillator tube envelope. However, initial tests indicated that with only a slight improvement in mounting and housing, the conventional tubes could be made to function and survive in the environment which was then available.

Reaction sensitivity tests of different plastics with antenna caps 42 of various sizes, located either on the inside or on the outside of the plastic housing 221, indicated the electrical advantage of the outside cap. This appears obvious when it is considered that for a given plastic insulator, the outside cap 42 is extended a quarter inch or more in length, is not surrounded by a plastic material having some loss, and is farther removed from the near field of the oscillator coil 64'. The outside cap 42 also offers some measure of mechanical protection to the'extremity of the plastic housing 221. The outside antenna cap 42 was, therefore, favored for experimental fuzes 12 which were shot in field tests. Staking pins 242, as shown in FIG. 2, are utilized to hold the antenna cap 42 in position.

In order to protect the fuze 12 while in the bore of the gun, a protective cap 232 is provided as shown in FIG. 4. It can be seen that if the projectile 10 has its base end turned to a smaller diameter, it can be externally threaded as shown at 230. The external fuze housing 221 projects rearwardly beyond the base. The cap 232 is screwed on the threaded section 230 and it is made of very thick steel. It has an internally threaded portion 235 that screws on the threads 230 of the projectile l0, and a shoulder 236 that abuts the base 14 of the projectile 10 when the threads are screwed fully home. A thin coating of Miracle cement in the joint assures gas-tightness. There is a cavity 237 in the cap 232 of sufificient size to avoid contact with any portion of the fiize housing 221.

Cap 232 is provided with holes 238 in its base, which will admit gases into chamber 237, and thus subject the fuze housing 221 to the pressure produced by the propellant gases when the gun is fired.

This cap 232 is efficacious in protecting the fuze 12 mechanically from impact injuries when the spent projectile falls base down after vertical test firing and it also protects the fuze from the gases in the interior of the gun tube.

It is to be noted that the inner parts of the fuze 12, within the projectile, may be substantial conventional, with the exception of requiring proper attention to whether the threads should be right or left-hand.

In actual operation, the fuze 12 is assembled to the projectile 10, as shown in FIG. 1, with the cap 232, being in position, as discussed above. The projectile 10, with its shell casing (not shown), is then loaded into the breech of a gun, where it is fired at a suitable target. The cap 232 separates from the projectile in aerial flight, while the shell casing remains in the breech of the gun.

Upon activation of the oscillator 26 of the fuze 12, the antenna 42 radiates an electromagnetic signal into space. This signal is reflected by the target, and is received by the antenna 42 and the oscillator 26 functioning as a detector. The detected signal is then amplified by the two stage amplifier 36, rectified by triode 50, and is fed to the control grid 142 of the thyratron 52 where it is used to overcome a fixed negative bias on the grid 142 of the thyratron. When the negative bias on the control grid 142 of the thyratron 52 is overcome, the thyratron 52 is fired, thus discharging a capacitor in the firing circuit, which includes the electrical squib 54.

Upon ignition of the squib 54, the auxiliary detonator 40 is exploded. This detonator 40 explodes the tetryl booster 41, which, in turn, explodes the main explosive charge contained in the projectile 10. The fragments from the exploding projectile 10 upon striking the target, destroy it.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A hollow projectile having an explosive charge therein, said projectile having a rearwardly facing portion with an aperture formed therein, a closure plate for said aperture, a proximity fuze carried by said closure plate and including an oscillator and an antenna in the form of a conical structure projecting rearwardly from said closure plate, mounting means on said closure plate for supporting the remainder of said proximity fuze within said hollow projectile, and connecting means including a plurality of tapered pins engageable with and passing through said closure plate for electrically coupling said oscillator and antenna with the remainder of said proximity fuze. 

1. A hollow projectile having an explosive charge therein, said projectile having a rearwardly facing portion with an aperture formed therein, a closure plate for said aperture, a proximity fuze carried by said closure plate and including an oscillator and an antenna in the form of a conical structure projecting rearwardly from said closure plate, mounting means on said closure plate for supporting the remainder of said proximity fuze within said hollow projectile, and connecting means including a plurality of tapered pins engageable with and passing through said closure plate for electrically coupling said oscillator and antenna with the remainder of said proximity fuze. 